New patient on the table.
I got an old 1979 Apple II+ off eBay with a non-working 'O' key. This keyboard is the one with all the separate soldered individual keyswitches and integrated encoder board (it's not the separate one with the 25-pin cable).
I verified this was the only problem and disassembled. Tried to clean it with some "tuner cleaner" and that didn't help, so I checked with a meter and pushing the "O" key does short the contacts on the back of the keyboard, so the key "works". I put it back together again and notice now that the keys aren't "correct" anymore (and "O" still does nothing). Typing the letters works, but numbers and symbols are all wrong. Pressing 1 prints Q, 2 prints R, 3 prints S, etc. It's really strange. You can't even type the "return" key because it prints "M".
Anyone seen this problem before? The board looks clean- I don't see bad traces or cracks, but I can reflow the whole thing to see...